Leakage/creepage distance for surge arrestors

[Power0020]

I noticed in a 220 kV substation specs that the owner stated that the creepage distance for surge arrestors to be 45 mm/v while for other insulators kept at 35 mm/kv.

It looks greater than maximum IEC polluted situation but it is normal to find these figures around middle east where pollution and very low annual precipitation levels are common.

Why the creepage distance for surge arrestors are higher than other insulators? I remember that the SA housing usually has a shorter length (and accordigly BIL, to ground) compared with other insulators, this is used to increase the electric field strength and provide more protection to equipment to be protected beyond the SA.

Any clues?

 

[cuky2000]

Surge arrester behaves similarly than any insulator at power frequency voltage and the contamination level of the operating environment. However, manufacturers design the surge arresters housing to also withstand lightning and switching impulse and this will drive the creepage distance above other design parameters.

For 220 kV, the unified specific creepage distance of a surge arrester range approximately from 44 to 56 mm/kV (Us/1.73) as indicated in the table below and the technical information data from one recognized manufacturer. Any arrester rated for a maximum operating voltage of 245 kV will meet your client spec of 45 mm kV.

Beware that for proper arrester selection you should take in consideration the maximum system voltage phase-to-ground, the MCOV rating, system grounding, energy dissipation, equipment protective margin, among other parameters.


For details, see the info and the link below.

https://library.e.abb.com/public/be...f/Surge Arresters Buyer's Guide Edition12.pdf